The numbers on U.S. interstate freeway indicators could appear random, however they’ll really be an vital navigation instrument. This brief video reveals the way it all works.
For starters, the interstate system is split into majors, mediums, and minors. East-west majors get double-digit numbers ending in zero, with larger numbers for the extra northern routes. That is why the northernmost interstate (connecting Boston and Seattle) is I-90, whereas the southernmost (connecting Jacksonville, Florida, and Santa Monica, California) is I-10.
Interstates aren’t all the time sequentially numbered, nevertheless. I-50 and I-60 do not exist as a result of these numbers had already been utilized by highways that have been a part of the pre-interstate system (which additionally birthed Route 66).
The north-south interstates additionally get double-digit numbers, however this time ending in “5” to point their route, and decrease numbers for the routes furthest west. That is how the interstate connecting Maine and Florida grew to become I-95. The route connecting California and Washington State is named I-5, a single-digit quantity, however nonetheless acceptable for this most-westerly route.
Interstate minors diverge from the majors and get three-digit numbers. The final two digits match the foremost they diverged from. If the primary digit is even, meaning the minor will ultimately reconnect with that main. For instance, I-670 splits off from I-70 in Kansas Metropolis, Missouri, and reconnects in Kansas Metropolis, Kansas.
If the primary digit in a minor-route quantity is odd, the freeway does not reconnect with the interstate it began from. That is why these highways are typically known as spurs, though they’ll additionally join with a unique interstate. As a result of this technique solely permits for restricted quantity decisions (1-9 plus the guardian freeway’s quantity), there are a lot of duplicate minors. Each Maryland and Massachusetts have an I-495, for instance.
Lastly, interstate mediums use double-digit numbers, with even numbers indicating east-west routes and odd numbers for north-south routes. Nonetheless, among the numbers are duplicated. That is allowed so long as the routes in query are far sufficient aside to keep away from confusion.
So whereas there are some exceptions, it’s doable to take a look at an interstate quantity and determine which route you are touring, and what main highways the smaller interstates connect with. Maintain that in thoughts throughout your subsequent street journey.